The present invention relates generally to video processing apparatus and methods for use with imaging systems and the like, and more particularly to a system and method which implements scene based nonuniformity compensation of the detector elements of a staring infrared focal plane array imaging system.
Nonuniformity compensation for staring infrared focal plane array imaging systems is generally necessary to adjust each of the detector elements so that their outputs will appear to be identical. Implementation of nonuniformity compensation results in low fixed pattern noise in the infrared image. Consequently, subsequent processing of the infrared image to determine targets or other scene information can operate at low signal to noise ratios and consequently long standoff ranges.
Conventional nonuniformity compensation methods have employed such techniques as storing compensation terms in memory or utilizing spiral scan techniques, for example. The memory storage technique involves viewing a uniform infrared source under laboratory conditions and storing the compensation terms in memory. This technique is far from efficient, since if the average temperature of the scene changes by a few degrees Celsius with respect to the temperature used to calibrate the compensation terms, then the compensation is not correct and a high fixed pattern noise imager will result. Spiral scanning techniques involve moving the detector line of sight in a spiral pattern to smear the image and provide a somewhat uniform scene on with the nonuniformity compensation can be made. However, one major disadvantage of this technique is that the seeker has to stop providing imagery to the tracker during the flight to perform this function. In addition, blockage of the image is required to provide a uniform input to the detector using a reference source. Alternatively, a shutter may be employed as a means of providing a uniform reference source on which compensation terms may be calculated. However, the shutter also blocks the image during the referencing procedure. Accordingly, these techniques have limitations which hamper their use in infrared imaging systems.